Create decryptable encrypted string

Question

I need to store some encrypted data and then (in second time) read the original value, I don't need very strong encryption, just much as the user can't be able to manipulate those string(s).

I'm trying this code:

 public static string Encrypt(string plainText)
 {
     if (Settings.LicenseOK())
     {

         byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

         var symmetricKey = Aes.Create();
         //symmetricKey.Mode = CipherMode.CBC;
         symmetricKey.Padding = PaddingMode.Zeros;
         ICryptoTransform encryptor = symmetricKey.CreateEncryptor();
         using MemoryStream ms = new MemoryStream();
         using CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write);

         cs.Write(plainTextBytes, 0, plainTextBytes.Length);
         cs.FlushFinalBlock();
         ms.Flush();
         return Convert.ToBase64String(ms.ToArray(), Base64FormattingOptions.None);

     }
     else
         throw (new Exception("Errore nella DLL GDWS"));
  }

  public static string Decrypt(string cipherText)
  {
     if (Settings.LicenseOK())
     {
         byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

         var symmetricKey = Aes.Create();
         //symmetricKey.Mode = CipherMode.CBC;
         symmetricKey.Padding = PaddingMode.Zeros;

         byte[] plainTextBytes = new byte[cipherTextBytes.Length];

         ICryptoTransform decryptor = symmetricKey.CreateDecryptor();
         using MemoryStream ms = new MemoryStream(cipherTextBytes);
         using CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read);

         cs.Read(plainTextBytes);
         return Encoding.UTF8.GetString(plainTextBytes);
     }
     else
         throw (new Exception("Errore nella DLL GDWS"));
 }
}

But every time I encrypt a string, the encrypted one changes (I think it has to remain the same or it can't be decrypted), and I cannot revert the process (decryption) (the decryption process takes to an incomprehensible yet always different string).

Please help me.

Answer 1

You have to preserve the same key between encryption and decryption.